The CBS era strats had a tailpiece that was single a zinc alloy casting (except for the individual saddles, of course). A steel inertia block can't be fitted, unless you were to mill off the casting and add the proper countersunk holes through the bridgeplate to accomodate it. That's a machine shop job.

The Fender Vintage reissue (US made) guitars, both '57 & '62, are fitted with the vintage style tailpiece which has a the bridge plate bolted to a separate inertia block. It includes the full sized steel inertia block. So retrofitting the same type of block from Callaham won't improve anything.

There are japanese made vintage style tailpieces that have full size inertia blocks but are made of a zinc alloy casting. (For instance, the japanese 50s &60s strats, the vintage trem from Stewart MacDonald, and the same from Allparts, possibly TexMex strats, also.) If the mounting screw holes through the bridge plate line up, the Callaham steel block can be retrofitted for a slight improvement in sustain.

Guitars that would benefit greatly from a larger inertia block would be the mexican standard strats and all them friggin floyd roses with the wimpy tone. Trouble is, either the holes don't line up or the thing is a single casting. I think Callaham has a specially drilled model to fit the AmStd two point pivot trem, which should be a noticeable improvement over the stock block.

These sustain improvements are only noticeable if the trem tailpiece is floating. If you have it held against the body anyway, sustain is greatly improved and the block mass doesn't much matter.